Congress starts its new session tomorrow, but the fireworks have already gone off in the Senate. In a Washington Post op-ed, incoming Sen. Mitt Romney laid out his approach to Donald Trump, promising to support policies which deserve support but not to defend policies and behavior that don’t. Before getting to his point, however, Romney emphasized that Trump has not “risen to the mantle of office” in his first two years, and looked particularly bad over the last month:

The Trump presidency made a deep descent in December. The departures of Defense Secretary Jim Mattis and White House Chief of Staff John F. Kelly, the appointment of senior persons of lesser experience, the abandonment of allies who fight beside us, and the president’s thoughtless claim that America has long been a “sucker” in world affairs all defined his presidency down.

It is well known that Donald Trump was not my choice for the Republican presidential nomination. After he became the nominee, I hoped his campaign would refrain from resentment and name-calling. It did not. When he won the election, I hoped he would rise to the occasion. His early appointments of Rex Tillerson, Jeff Sessions, Nikki Haley, Gary Cohn, H.R. McMaster, Kelly and Mattis were encouraging. But, on balance, his conduct over the past two years, particularly his actions this month, is evidence that the president has not risen to the mantle of the office. …

Furthermore, I will act as I would with any president, in or out of my party: I will support policies that I believe are in the best interest of the country and my state, and oppose those that are not. I do not intend to comment on every tweet or fault. But I will speak out against significant statements or actions that are divisive, racist, sexist, anti-immigrant, dishonest or destructive to democratic institutions.

Given the sharp criticism in Romney’s column, one might have expected an overwhelming response from Trump this morning. Instead, the reply only measured a 5.0 on the Trump-Twichter scale. Aside from a shot about Romney being the next Jeff Flake, the rebuttal came across as relatively measured and … not exactly friendly, but at least not entirely hostile either:

Okay, so it’s not all that lit. In fact, it’s not really much different than what Romney has said all along on the campaign trail, where he took care to distance himself from Trump but not alienate Trump’s smaller set of supporters in Utah. Trump probably figured the same thing, which might be why he didn’t produce a multi-tweet response closer to a 9.0 on the scale.

Still, it was enough for CNN to set off the sirens:

CNN pulls together a roundtable of analysts to answer one question: why did Romney write this? Kevin Madden, who has worked with Romney for years, can’t quite figure it out, and neither can anyone else. It can’t be, as GOP strategist Doug Heye suggests, a drawing-a-line-in-the-sand moment. Romney’s been drawing them all along. If Romney had run on a Trumpist line for the Senate, then that might explain this op-ed, but Romney ran on precisely this same message since launching his Senate run. Madden also notes that none of this is new, with the exception of the point about what happened over the last month. Romney had already issued his “statement of principles” during the Senate campaign, repeatedly. What’s the point of doing it again?

The only answer that makes any sense is to goose the GOP with the thought of a primary challenge. It’s 2019, after all, and Elizabeth Warren has already opened up the presidential season. Could Romney be thinking that he can run against Trump for a second shot at the presidency? By next year Republicans might entertain the thought of a primary challenge to an incumbent president, but it seems verrrry doubtful that the GOP would turn its lonely eyes to the man who lost a winnable election in 2012. Trump hasn’t risen to the mantle of office, but Romney didn’t do so well in rising to the mantle of competitor when it counted, either — a point Trump makes with little subtlety in his Twitter response.

Update: Allahpundit will have a lot more on this in the next article, but um … holy moly, as Karen Tumulty put it:

The next Romney family reunion will be a gas, right?